1. Field
One embodiment of the invention relates to a video signal processing device and a video signal processing method for performing high band emphasis processing on a video signal based on a brightness histogram.
2. Description of the Related Art
It is known that flat-panel large screen displays have been developed for use in television broadcast receivers in recent years. Such a large screen display performs signal correction processing by using the brightness component of a video signal in order to display a crisp video picture.
JP-A-2006-33469 discloses a configuration where contour correction is made as part of signal correction processing. In the disclosed configuration, the gradation correction characteristic setting part evaluates and determines the pixel frequency distribution of a brightness level histogram and emphasizes the contrast of a gradation correction characteristic in a region at a brightness level with higher pixel frequency. The gradation correction characteristic setting part evaluates and determines the pixel frequency distribution of an edge level histogram and weakens the contrast emphasis effect of a gradation correction characteristic in an almost flat level region with gradation. The problem with JP-A-2006-33469 is that an effective control method with sufficient precision is not disclosed concerning the high band emphasis (sharpness) processing of a video signal as another target of signal correction processing. To be more precise, uniform sharpness is given across the screen but finer high band emphasis processing that corresponds to the brightness level of a particular region of the screen is not available.
In addition, JP-A-2005-175735 discloses a configuration where contour correction is made as part of signal correction processing. Brightness distribution is evaluated and determined in a control circuit 4 and contour correction is weakened in a brightness level region with high distribution frequency in a contour correction circuit 5. As a result, possible noise is suppressed. A problem with the method disclosed in JP-A-2005-175735 is that contour correction is simply weakened over the range of brightness level having for example a larger number of pixels than a predetermined threshold h1 as a method for evaluating/determining the brightness distribution. To be more precise, an effective control method with sufficient precision is not disclosed concerning the contour emphasis, or in other words, the high band emphasis (sharpness) processing of a video signal. For example, in case a steep crest appears in the brightness distribution obtained, the crest indicates a region where a change in the brightness is minute and plain (uniform). There is no way to seek for the possibility of noise reduction effect suited for such a region.